Surely you only pay tax on any amount that you are over the threshold Steve, which is the same for anyone pensioner or not?
My private pension is already over the threshold so I was already paying tax on that so when my state pension kicked in in June it sent me further over the threshold. The extra tax I now owe is taken from my private pension so my state pension is paid in full each month. I have recently received a letter informing me that my tax will be more from April 1st but I presume that is because they know I will get a rise in my state pension of 4.8% (which I have also just been informed of) and I will get a similar rise on my private pension which will also attract more tax.
(I think that's how it works but could be wrong)